The long-term goal of this project is to elucidate basic principles of chemosensory perception. It seeks to explain at the molecular and cellular levels how chemosensory information is encoded. The experimental plan takes advantage of the fruit fly Drosophila melanogaster as a model system, which allows incisive molecular genetic analysis of chemosensory receptors and neurons and of the functions that they perform. Olfaction and taste have been considered as separate senses since the time of Aristotle. This project examines the coding of odorants by the taste system; it attempts to bridge the two systems in an unprecedented way. The first aim analyzes physiological responses elicited from taste neurons by odorants in solution. The aim is designed to elucidate principles by which the taste system encodes odorant quality and quantity. This aim could provide a new dimension to our understanding of how odorants are detected and discriminated in a natural context. The second aim analyzes behavioral responses elicited by odorants via the taste system. Four behaviors will be investigated, using olfactory-deficient animals and a diverse panel of odorant solutions. The relative roles of the olfactory and taste systems in mediating behavior will be examined. The results of this aim could reveal that a surprisingly wide variety of odorants can drive behaviors via taste circuits. The third aim seeks to identify taste receptors that underlie the responses to odorants. The aim tests the hypothesis that some of these responses depend on the Ionotropic Receptor (IR) coreceptor IR25a, together with other IRs with which it acts. The proposed study should reveal whether an individual taste neuron detects different odorants via different receptors, and whether an individual odorant is detected by multiple receptors across multiple neurons. This aim may advance in a new way our understanding of the molecular logic of chemosensory coding. Diseases carried by insects afflict hundreds of millions of people each year. These insects detect their human hosts, their food, and their mates largely through their chemosensory systems. This project may lead to the development of new kinds of insect repellents that act on the taste systems of insect vectors of disease. Such repellents could be useful in controlling these insects and the diseases that they transmit.